Rannoch-rush seems harmless enough, but it has been a thorn in the side of those who have tried to classify it. It was first included in the Arrowgrass family (Juncaginaceae), but with regards to the fruit and flower in particular it was more like a lily. Eventually it was given a family of its own, of which it is the only member.

Rannoch-rush grows on the edges of puddles in sunken, nutrient-poor bog mosses, muddy bare ground and the saltier coastlines. It floats in wet peat a few centimetres deep with the help of its creeping, air-filled rhizome. The species is one of Finland’s most common bog plants and in its habitats it is many times the dominant – and often the only – vascular plant. It is able to form large, dense stands. Rannoch-rush looks quite modest, and the most noticeable thing about it its follicles, which look relatively large and shiny compared to its overall fragility. If the raw fruits are squeezed they give off a smell like chlorine, reminiscent of swimming baths. Rannoch-rush’s flowers are wind-pollinated, which could explain their modest colour and the way its anthers shake off pollen in the breeze at the end of long filaments. Rannoch-rush is not usually able to flower every year in its meagre habitats.

The tip of rannoch-rush’s leaves – including its subtending bracts – have a spoon-like hollow with a small water-hole where the leaf’s main vein ends. Drops of water can be seen falling from it, especially in damp weather. This is how the plant keeps water pumping through it, even when its habitat is usually too damp for efficient evaporation. In this way the plant is able to collect sufficient nutrition from the bog-water in its nutrient-poor habitats.